James Chadwick discovered neutrons in the year 1932.
After the discovery of electrons and protons, it was revealed that the mass of an atom cannot be calculated based on the number of electrons and protons present in it.
There may be some other particle present in it.
This problem was solved after the discovery of 3rd subatomic particle-'neutron' by James Chadwick.
It was found that all atoms of elements contain neutrons except ordinary hydrogen atoms.
The neutron is a neutral particle found in the nucleus of an atom. It was denoted by the symbol 'n'.